High concentrations of ice crystals have been identified as a hazard to jet aircraft engines and aircraft external sensors such as pitot (airspeed) probes. It was only in the last 5-10 years that enough previously unexplained engine and aircraft problems were collected together, studied and attributed to ice crystals.
Ice crystals are a major issue for general and commercial aviation, especially for large transport category aircraft because they operate at higher altitudes and consequently spend a greater proportion of their time operating in the presence of ice crystals. The icing problem for these aircraft has recently become more acute because of the tremendous growth in commercial aviation.
It is well known that the total water content in a cloud includes both unfrozen droplets (liquid water) and frozen water in the form of ice crystals. The ice water content (IWC) in the cloud can be determined by comparing the liquid water content (LWC) to the total water content (TWC). That is, IWC=TWC−LWC.
It is also known that one way to determine LWC alone, for example, is to use a heated sensor element that tends to “retain” liquid water but ignore ice crystals. Water “retained” by the sensor is continuously evaporated by a portion of the applied power. The total power used to evaporate the liquid water, after corrections for cooling from moving air alone, can provide a measure of liquid, water content.
Likewise, TWC is estimated by using a sensor that tends to retain both liquid water and ice crystals. The retained ice crystals (after being converted to water) and the liquid water “retained” by the sensor are both continuously evaporated by the applied power. The total power used to evaporate the net liquid water, after corrections for cooling from moving air alone, gives a measure of the total water content.
It is then a matter of performing the subtraction TWC (power)—LWC (power) to determine if the power difference associated with an amount of ice crystals equals or exceeds a predetermined amount.
A cloud water measurement system which uses a compensation sensor to account for the differences between dry air cooling of the cloud water sensors used is described in U.S. Pat. No. 7,643,941, the subject matter of which is incorporated by reference as if fully set forth herein.
However, further developments are believed achievable. For example, a robust device that provides a warning of the presence of threshold amounts of ice crystals using principles outlined herein and without the need for a separate sensor to compensate for cooling due moving air alone, is desirable and achievable by the invention disclosed herein.